Fast math arithmetic game

Test your ability to quickly solve examples in mind.
About the game:
Mathematical game to test and develop their skills quickly solve examples in mind.
The game has three levels of varying difficulty.
Sets your record and compete with friends.
This game may be suitable for children and adults as to be able to quickly figure in mind it may take perhaps all students in school, at university already is at work, or because he simply decided to improve their ability to quickly add and subtract in mind, because the ability to quickly count is the ability that can be improved in certain situations do without a calculator.
In the game you have 15 seconds to solve an example.
You can choose the level of difficulty Easy, Normal and Hard.
At each level, different numbers, such as the Easy level will not be more than 100 numbers which you need to perform mathematical operations, while Hard level will be a number from 1000-10000.